Search

The last decade has witnessed a rapid surge in application of body sensor net-works, especially in the domains of military, healthcare and fitness. In suchnetworks, wearable wireless sensor devices are used to measure and communi-cate a subject’s vital signs (such as heart rate, body temperature, blood glucoselevel, etc.) Security, in this context, is a critical issue as these devices deal withpersonal health data, requiring strict privacy and confidentiality. However, tra-ditional secret-key generation mechanisms (such as Diffie-Hellman) are typicallycomputation and power intensive and not suitable for resource-constrained sen-sor devices. This thesis aims at realizing a practical and low-cost secret keygeneration mechanism for wearable sensor devices.First, we investigate a secret key generation mechanism that extracts sharedsecret keys using properties of the near-body wireless channel between two com-municating parties. For a fully body-worn scenario, our experimental results,using off-the-shelf IEEE 802.15.4 devices, indicate that this approach is feasiblefor dynamic scenarios where communicating devices are placed in non-line-of-sight positions on the body. We also suggest an enhancement for existing keygeneration mechanisms using a filtering mechanism which considerably reducesbit mismatches.Second, we employ a channel hopping technique to decorrelate secret bit ex-traction. Due to fast sampling rates, successive samples of channel properties arecorrelated in time, yielding weak keys with reduced entropy. To overcome this, weuse channel hopping to increase channel diversity. We conduct extensive experi-ments to show that channel hopping increases frequency diversity and effectivelydecorrelates successive channel samples and thereby dramatically improving thestrength of the secret key. Furthermore, we identify key parameters affectingperformance, namely channel spacing, the number of available channels, and useractivity. We show that it is possible to dev

Our long-term scientific goal is to better understand the mechanisms by which mixing occurs in the ocean so that we can develop improved parameterizations of mixing for ocean models. Mixing within the stratified ocean is our particular focus, as the complex interplay of internal waves from a variety of sources and turbulence makes this a current locus of uncertainty. In this project, our broad focus is on the energy sources of nonlinear internal waves (NLIWs) in a complex environment of strong internal tides and abrupt topography (continental shelf and slope). We expect a rapid evolution of internal tides and NLIWs, and aim to understand their dynamics, energy cascade, and role in mixing. The primary objectives of the project are as follows: (1) to identify the generation sites and understand the generation mechanism of NLIWs, (2) to understand the evolution of NLIW interactions with abrupt topography, (3) to quantify the energy budget and energy cascade from internal tides to NLIWs, and (4) to quantify the seasonal variation of the energy of NLIWs near Dongsha Plateau in the northern South China Sea (SCS). Our particular interest is to understand the energy cascade from barotropic tides, internal tides, and NLIWs to turbulence mixing in the northern SCS, and to understand the evolution of NLIWs interacting with the shoaling continental slope. Our approach is to take direct observations of NLIWs near Dongsha Island, where NLIWs are often captured in satellite images. Primary platforms include an ADV Lagrangian Float; an array of bottom-mounted ADCP moorings; and shipboard EK500, marine radar, ADCP, and CTD. Our main goals are to quantify the energy budget and evolution of NLIWs across the rapidly shoaling continental slope and the gentle plateau near Dongsha Island, and to quantify the seasonal variation of NLIW characteristics.